Clock assemblies are used in many diverse types of assemblies and systems, such as within vehicles, to maintain and to selectively display the "time-of-day" and to perform other time dependent functions and operations.
Typically, many of these clock assemblies include a microcontroller and/or microprocessor which utilize the relatively high resonant frequency signals generated by a crystal oscillator to periodically produce an estimation of the time-of-day. Particularly, the frequency of these oscillator generated signals is typically reduced or "scaled" in order to allow for the estimation of desired and discrete intervals of time, such as a minute or a second, to be achieved. While these clocks do maintain and selectively display the time-of-day, they suffer from some drawbacks which reduce their respective accuracy. Importantly, even relatively small inaccuracies, if not properly corrected or compensated, will accumulate over time causing the creation of relatively large undesirable errors.
For example, the resonant frequency of the oscillators often drifts or varies, thereby causing the calculated time-of-day to be inaccurate and requiring the clock to be periodically and manually adjusted.
Further, due to manufacturing intolerances, the resonant frequency of most commercially available and relatively cost effective crystal oscillators typically varies from about 20 pulses or parts per million ("ppm") to about 500 ppm from their respective specified or "published" frequencies. These tolerance type variances or "calibration type errors," if uncompensated, will also result in significant errors in the time-of-day kept by the clock.
Moreover, these crystal oscillators typically produce a resonant signal having a frequency which is not divisible by an even number, thereby creating certain "fractional errors" when used to produce discrete ("minute" or "second") time estimates. These "fractional errors" accumulate over time and cause significant inaccuracies in the time-of-day kept by the clock.
While certain assemblies and devices have been proposed to compensate for these oscillator related errors, such as the use of variable load capacitors, they undesirably and respectively increase the overall cost and complexity of the clock assembly. Further, none of these prior compensation assemblies typically provide for fractional error correction.
There is therefore a need for a new and improved time-of-day clock assembly which provides a relatively accurate measure or estimate of the time-of-day and which is relatively cost efficient.